Volvo bets on new PowerPulse, not 48V, for turbodiesel boost assist

2016-07-10
Stuart Birch

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Volvo is using a blast of compressed air to boost torque delivery and exorcise turbo "lag" of its new D5 diesel engine. It's a comparatively simple technology solution that works very effectively, as company engineers demonstrated to Automotive Engineering on a lengthy and often demanding test drive of the D5-powered V90 station wagon in southern Spain.

Volvo has dubbed the novel, heavily patented diesel air-delivery system "PowerPulse." It serves as a cost-effective alternative to using a 48-V hybrid system with electrically-driven turbocharger or supercharger to rapidly spin up turbines at low engine revs.

Volvo powertrain engineers spent more than three years developing PowerPulse, on the same critical path as the D5 engine. The 2.0-L 4-cylinder direct injected diesel delivers a claimed 173 kW (232 hp) and 480 N·m (354 lb·ft). A lower-powered D4 version producing 140 kW (188 hp) and 400 N·m (295 lb·ft) without PowerPulse also is available.

A simple, compact system

On the road PowerPulse literally blows into action, helping the V90 wagon accelerate from standing start to 100 km/h (62 mph) in 7.2 s which, bearing in mind the car’s power output and 1817-kg (4006-lb) curb weight, is brisk but not exceptional. The car’s automatic transmission is an 8-speed Aisin. No manual gearbox is offered.

Powertrain Program Manager Fredrik Ulmhage said the PowerPulse system was conceived entirely in-house. “No one else has it," he asserted. "We have a 4-cylinder diesel strategy (as we have for our gasoline engines) and decided we needed to deal with any turbo lag, getting the turbo running before exhaust pressure built.

"So basically, we push compressed air into the exhaust manifold as the driver pushes the accelerator pedal and within milliseconds the turbo spools up,” Ulmhage explained.

This can happen twice consecutively, with virtually no pause between applications. If a third rapidly-required consecutive step-off is needed (regarded as an extremely rare likelihood), it would take a couple of seconds for the system to re-charge to provide a further pulse. A small compressor squeezes air into a 2.0 L tank at a pressure of 12 bar (174 psi), with a magnetic valve controlling the action phase of the system.

Volvo's D5 engine is configured with two BorgWarner turbo machines sized 38 mm and 53 mm, respectively and operating sequentially. Engineers claim the system reaches its peak 150,000 rpm from idle in 0.3 s. “When we matched the system against competitors’ 6-cylinder diesel engines from stationary, our new 4-cylinder was ahead of them for up to 50 to 60 meters,” noted Ulmhage. He confirmed that Volvo's XC90 SUV will also be offered with PowerPulse. And the system is likely to be fitted to other upcoming models.

The PowerPulse system adds about 10kg (22 lb) to the base diesel engine. It fits into a convenient underhood space behind a headlamp housing. Volvo engineers are investigating lightweight materials that could be used to reduce mass of the pressure tank.

Volvo has a series of high-priority technology programs with the emphasis on hybrid efficiency and is aiming to take gasoline powertrains much closer to diesel fuel consumption potential.

A 3-cylinder gasoline engine is in the pipeline with a rated output expected to exceed 130 kW (174 hp). It will be used to power smaller Volvo models, bringing not only performance efficiency but also reduced unit cost compared to diesels, the cost of which rises as more engine controls and aftertreatment are incorporated to meet emission regulations.

Finally possessing a platform the delivers the structure and chassis dynamics necessary to deliver premium-class ride quality, Volvo development engineers are now focusing on NVH and other details, stated Product Manager Lars Lagström. He contrasted the company's Geely ownership to the years under Ford, when "there were always squeezed budgets" and "it was short-term everything." Ford, Lagström noted, "never understood Volvo."

Key initiatives have included in-house development of the independent rear suspension that helps the V90 deliver a poised ride on motorways or challenging curves. Interior design is another priority, with the impact of Vice President of Interior Design Robin Page (with Bentley until 2013) immediately evident when you step inside the new diesel wagon. It offers 560 to 1526 L (20 to 54 ft3) of maximum luggage volume including underfloor storage while avoiding any hint of utilitarian styling. Aerodynamics of the V90 models achieve a best of 0.30 Cd.

With the approach of the age of autonomous driving, the V90 and S90 offer Pilot Assist and adaptive cruise control, which team to provide semi-autonomous operation of steering, accelerator and brakes within lane markings at speeds up to 130 km/ h (81 mph). But it is not a fully hands-off system.